The principal aim of this project is to test the hypothesis of general multispecificity for the combining regions of antibodies and other kinds of receptors. Receptor sites should be capable of interacting with an occasional, disparately structured substance with an affinity high enough to affect biological function. Radiolabeled antibodies or solubilized receptors are passed through small, affinity chromatography columns. Accurate measurements are made of the retention (retardation) caused by the affinity adsorbent in the presence and/or absence of many, diverse, suitably large compounds. The resulting retention values are employed directly in calculating association constants, whose occurrence of frequencies provide a description of a receptor's multispecific character. Monoclonal antibodies from myelomas and hybridomas are currently being studied. In this study, large affinity probes that can be covalently bound to column matrices are being synthesized by systematic routes involving techniques used in peptide synthesis. Multispecific interactions will be usefully employed in extending the scope of specific affinity bases separations and assays. Multispecificity frequencies will play a role in understanding the specificity of immune responses.